1. Field of the Invention
This invention generally relates to four-stroke engine, and more specifically, to a lubrication device that is applicable to four-stroke engines.
2. Description of Related Art
In order to provide common portable work machines, such as lawn mowers, chain saws, and other trimmers with sufficient torque and long-term power, modern industry adopts designs that employ engines of internal combustion as power source. However, the foresaid portable work machines are commonly manipulated at various angles, for instance, a chain saw must be manipulated at various angles in accordance with a specific practical object to be cut, but not maintaining at a same angle; beside, to answer the manual manipulation demands of light weight and high rotation speed, two-stroke engines are preferable selections of internal combustion engine to four-stroke engines theoretically.
When a foresaid two-stroke engine is operating, it emits exhaust fume and takes in air at the same time; in this situation, the emitted exhaust fume contains some fuel unburned or incompletely burned, and it means that using the two-stroke engine will cause exhaust fume pollution; therefore, it cannot pass some of the standards and regulations of pollution emissions recently issued. On the contrary, four-stroke engines have fuel burned more completely and conform to the emission standards thus; in addition, four-stroke engines have less noise than the two-stroke engines while operating, and consequently, it is an inevitable trend of adopting four-stroke engines in the designs of power work machines.
Although four-stroke engines have advantages of less noise and lower emission pollution, they have disadvantage as well; cams and valves of the four-stroke engines require proper lubrication; therefore, a four-stroke engine must be integrated with a lubrication device; however, when a four-stroke engine integrated with a lubrication device and is applied to a work machine, such as a chain saw or others, due to the practical application environment, user is likely to manipulate the four-stroke engine at an extremely slanting or even upside down angle, and at this moment, lubricant stored inside crank case of the lubrication device is likely to flow into exhaust valves as well as flow path of air mixture in the combustion air, thereby further interfering with effective air combustion and causing engine oil leakage.
In order to overcome the existing drawbacks of four-stroke engines applied to portable work machines, some improved designs of lubrication device of four-stroke engines are provided according to claims of U.S. patents, for instance, U.S. Pat. No. 6,213,078, and U.S. Pat. No. 6,170,456, and others.
As shown in FIGS. 1A and 1B, which are diagrams of a lubrication device of four-stroke engines according to claims of U.S. Pat. No. 6,213,078; wherein, an oil hole 11 in communication with lubricant tank 12 is allocated underneath a cam room 10, and the lubricant recycles back to the lubricant tank 12 via the oil hole 11; manipulations of this kind of design at some sloping angles are likely to cause the lubricant to directly reflow to the valves via the cam room 10, and then flow out of the engine via a respiratory pipe between valve chamber and air filter.
As shown in FIG. 2, a lubrication device of four-stroke engines is disclosed according to U.S. Pat. No. 6,170,456, which mainly allocates a stirring chamber 14 on a long and narrow concave underneath the crank case 13, and also forms an oil hole 15 at a bottom of the stirring chamber 14 in communication with an engine oil tank; although this kind of design is capable of preventing massive lubricant from flowing into the crank case when the engine is at a slanting angle, it is not capable of providing other mechanical parts of machine, such as cam and gas valves and others, with effective lubrication when the engine is operationally turning over for a long time period; in addition, the traditional respiratory pipe that is externally connecting to air filter generally is not commonly allocated with filter therein, therefore, when the engine is operating at a slanting angle, lubricant is likely to flow out via the respiratory pipe, thereby causing problems of unnecessary lubricant consumption and air filter contamination.
Hence, it is a highly urgent issue in the industry for how to provide a lubrication device of four-stroke engines, which is capable of enabling lubricant to flow into valve chamber and cam room to provide effective lubrication, and meanwhile preventing massive lubricant from flowing into air-intake system and thus the cylinder, consequently causing engine extinguished, thereby allowing users to manipulate engine at various angles.